This specification relates to content distribution.
The Internet provides access to a wide variety of resources, for example, webpages, images, audio files, and videos. Such access to these resources has enabled opportunities for providing relevant additional content. One example of additional content is advertisements. For example, resources of particular interest to a user can be identified by a search engine in response to a user query. By comparing the user query to a list of keywords specified by a content item provider, such as an advertiser, it is possible to provide relevant advertisements (or other content items) to the user with search results.
Another form of online content serving is remarketing, which allows content item providers to choose particular content items to be shown to users who have performed certain actions at a publisher's website. For example, an advertiser can choose to show a particular advertisement to users who have recently visited the advertiser's website. As these users are likely interested in the advertiser's offerings, they are likely to be interested in the advertised product or service. Accordingly, remarketing can help drive online customers to the advertiser's website.